A film forming apparatus for performing a film forming process on a semiconductor wafer, which is a target substrate to be processed, by, for example, a chemical vapor deposition (CVD) method includes a susceptor serving as a substrate mounting table for mounting the wafer thereon, and the susceptor has a heating unit therein. Various film forming reactions are carried out while heating the wafer indirectly by means of heating the susceptor. The susceptor is made of a ceramic-based material such as AlN having a high thermal conductivity, and is capable of heating the target substrate up to a processing temperature of, for example, about 700° C. or higher.
Recently, a wafer size has increased to about 200 mm to 300 mm, and with the increase of the wafer size, the wafer tends to be easily warped due to a temperature variation during a heating process (temperature increasing process) for the film formation. Once the wafer is warped, misalignment of the wafer would be caused while the wafer is being transferred, and a wafer edge portion or the like would come into a contact with the susceptor, resulting in a damage or a particle contamination. Thus, it is very important to prevent the wafer from being warped in the process of heating the wafer.
In this regard, there is proposed a CVD film forming method which includes performing a first preliminary heating process while maintaining the wafer on substrate (wafer) supporting pins after the wafer is loaded into a processing chamber; and then performing a second preliminary heating process after the substrate supporting pins are lowered and the wafer is loaded on the mounting table (see, for example, Japanese Patent Laid-open Publication No. 2003-77863).
The method of performing two steps of preliminary heating processes disclosed in Japanese Patent Laid-open Publication No. 2003-77863 is advantageous in that the warpage of the substrate is prevented. However, since the preliminary heating process is performed in the state the wafer is distanced apart from the mounting table by being sustained on the wafer supporting pins for the purpose of avoiding a rapid temperature rise of the wafer, it takes time to complete the preliminary heating. Particularly, if a processing temperature is high above 700° C., a reduction of a throughput is inevitable. Thus, these problems need to be improved.